I've actually tried that today, I also tried that with the English E-Reader Rom which told me REGION LOCK.
What you're actually supposed to do is actually go to Pokemon Colosseum, say Yes to the first question, say No to the second question and than leave it at the 3rd Question until you start up the E-Reader and go to Communication -> Nintendo Gamecube. This will actually download the Pokemon Colosseum application card scanning data used to send data through the E-Reader to Pokemon Colosseum, after that go to Access Saved Data, then on the Screen, (which I DO NOT KNOW WHAT IT LOOKS LIKE (N) ) will say please Scan Pokemon Colosseum Double Battle E Stadium Card, then will say Please Scan Pokemon Colosseum Trainer Card. It will transmit the data, and than *BAM* the information is sent to Colosseum. THERE IS NO WAY you can scan the card, and save it on the Utilities Access Saved Data (Which is basically the cards information saved onto the E-Reader permanently until overwritten), HOWEVER you can transmit the Pokemon Colosseum Transmission Application, and save it onto the Access Saved Data which than can be edited in a .sav file created by VBA or Extracted by gba backup tool v0.21. I'm not much of a hacker, but hackers can decipher a way to scan Japanese Cards, or translate these cards through trial and error, than you can easily just print out these cards with a 1200 DPI resolution or Higher Printer, onto Photopaper, load the save onto the E-Reader with GBA Backup Tool 0.21 with the *deciphered* save and scan the *translated* Card onto the US version.
How do I know this? Both the Japanese and US Version of the game have something called carde_menu.fsys which is a file holding all the Data for the E-Reader and how it works. You can see that in the hex editor, all 20 trainer cards .bin files (information either that contains information matching the card, or information needed to activate the event) are listed and I'm sure the other 4 are somewhere in the game's file system (I Used GC ISO tool to Extract carde_menu.fsys). I cannot solicit ROMS and ISOS on this forum but I'm sure you may be able to find a rom on Colosseum and use GC ISO Tool to find some other things that pertain to this room in General and maybe Trainer Data, Trainer Text Dumps, Anything you may be able to find. Again, how do I know this? When Scanning a card in the E-reader it will access Sprites, Data, Information from the save file and the save file is actually basically the Game Information it is supposed to access. Pokemon Colosseum, DOES NOT have the type of save file that the e-reader creates, the memory blocks used to save Pokemon Colosseum is 48 which is about 3MB's of Save Data, which is used to hold Pokemon, Record Information, Gamecube Save Files were never designed to carry E-Reader information, rather record activated events, when you catch a pokemon in colosseum, it doesn't get written on the disk or on the save file, it was already on the disc, the memory card carries data the game reads to know which events have occured and what things the game has to access to show your progress, and how you played the moment you wrote to the memory card. Pokemon Colosseum, has ALL of the Card Data written in the game, in theory you can EDIT THE SAVE to activate the events in the Log Book. So, somehow, we need to extract the card .bin files out of Colosseum's disc data and onto the computer, and try to load e-roader dot codes in NO$GBA if it says this data only works for Pokemon Colosseum we CAN print out these files onto an E-reader code strip, scan it on a real E-Reader device, or if possible load it onto an emulator and SUCCESS. WE HAVE JUST MADE BETA/UNRELEASED INFORMATION RELEASABLE, people can actually download these files they can simply print out these Translated Cards or Salvaged HIDDEN card data and scan it onto an Official E-Reader or load it onto an Emulator and Success, we just beat Nintendo!
HERE IS A PICTURE OF THE FSYS's HEX Data, Possibly Useful.
DOWNLOAD LINK TO CARDE_MENU.FSYS
http://www.mediafire.com/?ma7fgjho3cc3vmm
Tools to Look For:
GC ISO TOOL
POKEMON COLOSSEUM DISC IMAGE
POKEMON COLOSSEUM JAPANESE DISC IMAGE
POKEMON COLOSSEUM JAPANESE E CARD FULL SET
HEX EDITOR
-TOOL THAT CAN EXTRACT .bin FILES FROM FSYS.
-TOOL(S) THAT CAN TRANSLATE E-READER CARD DATA
-TOOL(S) THAT CAN MANIPULATE POKEMON COLOSSEUM SAVE DATA
TOOL THAT CAN PRINT E-READER CARDS (have that already, just forgot the name)
EDIT: CARDE_MENU.fsys I used this Program http://hcs64.com/files/gcfsysd01.zip to extact the data
seems that the .bins were useless in the FSYS. But this program may be able to help us out, by extacting ALL FSYS's data!
EDIT 2: You may be able to modify the Japanese Pokemon Colosseum ISO to read the English E-Reader, but than you would still need
to get the english e-reader to read japanese e-reader information